Yttria-alumina compounds are known in the art and tend to be highly refractory (e.g., have a melting point above 1900.degree. C.) and extremely chemically inert.
Cockayne in "The Uses and Enigmas of the Y.sub.2 O.sub.3 -Al.sub.2 O.sub.3, Phase System" J. Less-Common Metals, 114, 1985, pp. 199-206, reviewed selected properties and uses of the three crystalline yttria-alumina compounds (i.e., Y.sub.3 Al.sub.5 O.sub.12, YAlO.sub.3, and Y.sub.4 Al.sub.2 O.sub.9) in the Y.sub.2 O.sub.3 -Al.sub.2 O.sub.3 system.
Methods of making single crystal Y.sub.3 Al.sub.5 O.sub.12 yttria aluminum garnet) fibers are known in the art. For example, U.S. Pat. No. 4,040,890 (Burru, Jr. et. al.), teaches a method of making a single crystal neodymium-doped yttria aluminum garnet fiber from a melt.
Processes for making amorphous or polycrystalline alumina or modified alumina fibers are also known. For example, U.S. Pat. Nos. 3,992,498 (Morton et. al.), 3,994,740 (Morton et. al.) 3,950,478 (Kensworth et. al.), 4,801,562 (Sowan et. al.), 4,929,578 (Sowman) teach alumina and alumina-based fibers derived from liquid chemical precursors. Although patentees suggest the modified alumina fibers may contain one or more metal oxides including yttria, it is not believed any of these references teach an alumina fiber having substantial amounts of yttria, it is not believed any disclose fiber compositions based on yttria-alumina compounds, nor is it believed any provide suitably compatible chemical precursors for incorporating substantial amounts of yttria into an alumina fiber.
U.S. Pat. No. 4,007,020 (Church et. al.) teaches a method of incorporating a metal oxide into an alumina body, wherein a precursor of the metal oxide is impregnated into a porous alumina body. The impregnated body is subsequently heated to form the metal oxide. Although patentees list yttria as one of many metal oxides which could be incorporated into an alumina body by their method, they provide no working examples of incorporating yttria into any alumina body, nor do they suggest a suitable, yttria precursor. Further, it is not clear from patentees' disclosure the maximum amount of metal oxide which can be incorporated into an alumina body by their method.
Ceramic abrasive grits containing alumina and yttria have been taught. For example, U.S. Pat. No. 4,770,67 (Monroe et. al.) teaches alumina-based ceramic abrasive grits comprising yttria in the range from 0.5 to 30.0 percent by weight. European Pat. Appl. No. 0293 163 (Wood) teaches alumina-based ceramic abrasive grits which may contain yttria in the range from 0.5 to 30.0 percent by weight. U.S. Pat. No. 4,964,883 (Morris et. al.) teaches a process for making iron seeded alumina-based ceramic abrasive grits which may contain yttria. Patentees, however, do not disclose or suggest an yttria-alumina fiber.